Substrate processing typically involves forming structures on a substrate by formation of a sequence of layers of material on a substrate. Often the layer formation processes involve heating the substrate, e.g., to anneal a layer of material. In the semiconductor industry, substrates are often silicon wafers that are 300 mm in diameter or less. Such substrates may be easily heated using standard semiconductor processing equipment.
In the past, photovoltaic devices, such as solar cells, were made on silicon substrates and processed much like semiconductor integrated circuits. Recently, however, in an effort to reduce the cost of solar cells, the solar cell industry has been trying to develop techniques for high-volume fabrication of solar cells, e.g. using roll-to-roll processing. Such techniques often use convective heating or radiative heating (e.g., with infrared lamps). Unfortunately, these prior art techniques often produce non-homogenous heating of the substrate. For example, in a standard furnace, a roll of devices would experience a large temperature gradient depending on whether the ‘layer’ in question is near the inside or outside of the roll. In addition, these heating techniques can be difficult to design and expensive to implement.
Thus, there is a need in the art, for a method of uniform heating of large area substrates.